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                        <h1 id="">引用计数器</h1>
<h2 id="">本小节知识点:</h2>
<ol>
<li>【理解】什么是引用计数器</li>
<li>【理解】引用计数器的作用</li>
<li>【理解】引用计数器的操作</li>
</ol>
<hr>
<h2 id="1">1.什么是引用计数器</h2>
<ul>
<li><p>系统是如何判断什么时候需要回收一个对象所占用的内存?</p>
<ul>
<li>根据对象的引用计数器</li>
</ul>
</li>
<li><p>什么是引用计数器</p>
<ul>
<li>每个OC对象都有自己的引用计数器</li>
<li>它是一个整数</li>
<li>从字面上, 可以理解为”对象被引用的次数”</li>
<li>也可以理解为: 它表示有多少人正在用这个对象</li>
</ul>
</li>
</ul>
<p><img src="images/a1/yyjsq.png" alt=""></p>
<hr>
<h2 id="2">2.引用计数器的作用</h2>
<ul>
<li><p>简单来说, 可以理解为:</p>
<ul>
<li>引用计数器表示有多少人正在使用这个对象</li>
</ul>
</li>
<li><p>当没有任何人使用这个对象时, 系统才会回收这个对象, 也就是说</p>
<ul>
<li>当对象的引用计数器为0时,对象占用的内存就会被系统回收</li>
<li>如果对象的计数器不为0，那么在整个程序运行过程，它占用的内存就不可能被回收(除非整个程序已经退出 )</li>
</ul>
</li>
<li><p>任何一个对象, 刚生下来的时候, 引用计数器都为1</p>
<ul>
<li>当使用alloc、new或者copy创建一个对象时，对象的引用计数器默认就是1</li>
</ul>
</li>
</ul>
<hr>
<h2 id="3">3.引用计数器的操作</h2>
<ul>
<li><p>要想管理对象占用的内存, 就得学会操作对象的引用计数器</p>
</li>
<li><p>引用计数器的常见操作</p>
<ul>
<li>给对象发送一条retain消息,可以使引用计数器值+1（retain方法返回对象本身）</li>
<li>给对象发送一条release消息, 可以使引用计数器值-1</li>
<li>给对象发送retainCount消息, 可以获得当前的引用计数器值</li>
</ul>
</li>
<li><p>需要注意的是: release并不代表销毁\回收对象, 仅仅是计数器-1</p>
</li>
</ul>

                    
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